text: There exists a wide range of characterization methods for COF materials. There are several COF single crystals synthesized to date. For these highly crystalline materials, X-ray diffraction (XRD) is a powerful tool capable of determining COF crystal structure. The majority of COF materials suffer from decreased crystallinity so powder X-ray diffraction (PXRD) is used. In conjunction with simulated powder packing models, PXRD can determine COF crystal structure.
  In order to verify and analyze COF linkage formation, various techniques can be employed such as infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. Precursor and COF IR spectra enables comparison between vibrational peaks to ascertain that certain key bonds present in the COF linkages appear and that peaks of precursor functional groups disappear. In addition, solid-state NMR enables probing of linkage formation as well and is well suited for large, insoluble materials like COFs. Gas adsorption-desorption studies quantify the porosity of the material via calculation of the Brunauer–Emmett–Teller (BET) surface area and pore diameter from gas adsorption isotherms. Electron imagine techniques such as scanning electron microscope (SEM), and transmission electron microscopy (TEM) can resolve surface structure and morphology, and microstructural information, respectively. Scanning tunneling microscope (STM) and atomic force microscopy (AFM) have also been used to characterize COF microstructural information as well. Additionally, methods like X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), and combustion analysis can be used to identify elemental composition and ratios.